Del Potro to mingle with the awesome foursome

In sporting terms, it is a blessing to see the top four players in the world as competitive as they are right now, but is time running out on how long Novak Djokovic, Roger Federer, Andy Murray and Rafael Nadal will be able to dominate the ATP Tour circuit?

With 35 grand slams between the four of them, Djokovic and Murray are currently the pair close to the peak of their powers after winning the last two slams. However, at the other end of the scale Federer and Nadal have seemingly lost the duopoly they once had when it comes to fighting it out for major honours, evident with Federer not winning a title of any kind in 2013 while Nadal continues to battle back from injury to regain his place in the top four.

In the past, there were undisputed champions. Jimmy Connors tussled with Bjorn Borg for that tag in the 1970s, then Ivan Lendl and Mats Wilander arrived in the 1980s. John McEnroe and Boris Becker added to the mix - stoking rivalries along the way. More recently Pete Sampras in the 1990s was comfortably ahead of the rest of the field, and despite their best efforts Andre Agassi and Jim Courier could not outgun the Pistol.

In the modern era the top four have shared grand slams and titles the world over, passing on the baton of "world's best player" along the way. Djokovic can currently argue he is the man to hold the accolade after winning three of the four majors in 2011, but Federer and Nadal have both reigned over periods of dominance in the past.

But how long until the latter two - in particular - fall away from the group?

With Djokovic beginning the year by lifting the Australian Open, the Serb at the age of 25 has established himself as the scalp everybody craves.

Murray - the man who defeated Djokovic to get his hands on his maiden slam in 2012 at the US Open - is only a week older than the world No. 1, and has shown he can take the fight to the best by finally joining the grand slam winners' circle.

Nadal, the undisputed King of Clay, announced his return from a seven-month injury layoff by storming to the BNP Paribas Open at Indian Wells, and looks like he is ready to challenge for honours once again. But the long-term condition of his knees continues to be a question mark, and the real test will come after the relative comfort of the clay court season as to whether Nadal is truly back to his brilliant best on all surfaces.

Federer appeared to be heading into a decline similar to the one Pete Sampras incurred before he retired in 2003, but the Swiss maestro's triumph at Wimbledon last year signalled a brief turnaround. However, with the legs getting older the big question is whether the 31-year-old can add another grand slam to his record tally of 17 in the near future before he calls time on his illustrious career.

If Nadal or Federer, or both, do fall away from the top table in the near future, spotlight falls on the rest of the players on Tour to create new rivalries.

The top four was briefly broken up when David Ferrer leapfrogged fellow Spaniard Nadal during his absence, but with the latter winning tournaments in Acapulco, Sao Paulo and Indian Wells Nadal has moved back into fourth position.

Based on results, it has been Ferrer who has been the most likely player to get himself into the formation of the top four. The 30-year-old has the spirit of a terrier and, in the absence of Nadal, has been picking up the pieces, highlighted by reaching the semi-finals of three of the last four grand slams and winning the Paris Masters.

However, a player gets judged on how many slams he has won, and that is where Ferrer comes up short, yet to reach a major final and a regular faller to the top four players when he has made it into the semi-finals.

Tomas Berdych, like Ferrer, is another player who has underperformed, which is surprising for somebody of his build. Possessing a booming serve and standing at 6ft 5in tall, the Czech is yet to make the next step forward despite having grand slam qualities. He tends to throw in the odd wobbly display and lets his guard down, and has not kicked on as many observers first predicted when finishing a runner-up at Wimbledon three years ago. Berdych has inflicted defeats on the top four in competitive matches, but when it comes to the majors - over five sets - he is yet to show the required consistency.

The player who has proved his capability of roughing up the top four is Juan Martin Del Potro. The Tower of Tandil was making all the headlines at Indian Wells after consecutive comeback victories against Murray and Djokovic en route to the final, and has the 2009 US Open as evidence for being a big-time player.

The Argentine blew Nadal off the court in the semi-finals and stunned Federer in the final at Flushing Meadows to become US Open champion, and at the time was the first player since Marat Safin in 2005 to end the grand slam dominance of Federer, Nadal and Djokovic.

A wrist injury cruelly ruled out a title defence for Del Potro and saw him miss a huge chunk of the 2010 campaign, and from losing his place in the top four and sliding to 485 in the world, Del Potro has put those dark days behind him and come back a much better player both mentally and physically.

Indian Wells demonstrated that and, although he lost out to Nadal in the final, he showed in a set and a half he could match what one of the top four players had to offer, using his weapon of a forehand to produce a catalogue of incredible shots that not even the lung-busting Nadal could get a racket on.

In the past, Nadal was a certainty to win the French Open given he has lost only one match and triumphed a record seven times on the clay courts of Roland Garros. However, with his knees still causing him grief, there will be opportunities for Djokovic, Murray and previous winner Federer, but unlikely for Del Potro as he is not quite comfortable on clay.

Del Potro's best chance of winning a second grand slam is more likely to be on the grass of Wimbledon or the hard courts of the US Open, as the speed of both surfaces suit his all-round hard-hitting game.

Grigor Dimitrov (billed as the new Federer) and Canada's No. 1 Milos Raonic have also shown flashes of brilliance and have a bright future ahead of them, and only time will tell whether they can announce themselves in the same way Djokovic, Federer, Murray and Nadal did by winning events.

But Del Potro is the man who can do the damage to the top four right now. He has the proof, belief, and ability to rain on their parade and reclaim a place which was once his.